Crystals of fatty acid esters, for example crystals of ethylene glycol distearate (EGDS), are products commonly used in cosmetic formulations, as agents for affording a certain amount of pearlescence and/or as thickeners and/or stabilizers. These crystals may be formed during the preparation of the cosmetic composition. However, for practical and economic reasons, they are often sold in the form of ready-to-use fluid concentrated ingredients, intended to be mixed with the other ingredients of the cosmetic formulation.
Processes for preparing fluid concentrated ingredients based on fatty acid esters are thus known. These processes are based on solidification of a compound based on a fatty acid ester by cooling an emulsion of the said compound, which is melted in water in the presence of surfactants. For the same emulsion, the properties of the crystals generated may depend on the cooling conditions. This step is conventionally performed in stirred reactors such as stirred tanks. Typically, the emulsion filling the tank is placed in contact with cold walls, for example via jacketed tank techniques.
For example, document DE 3617306 (Henkel) describes a process for preparing products based on a fatty acid ester in which a heated emulsion based on the fatty acid ester is cooled slowly, without flowing.
Documents DE 19511571 and U.S. Pat. No. 6,306,916 (Henkel) describe a process for preparing products based on a fatty acid ester, in which a heated emulsion based on the fatty acid ester is cooled slowly, without flowing.
Document EP 581193 (Hoechst) describes a process for preparing products based on a fatty acid ester, in which a heated emulsion based on a fatty acid ester is cooled slowly. The cooling is indicated as being able to be performed at about 0.5° C. per minute.
Document WO 9503782 (ICI) describes a process for preparing products based on a fatty acid ester, in which a heated emulsion based on a fatty acid ester is cooled slowly. The cooling is indicated as being able to be performed at up to about 0.25° C. per minute (15° C. per hour).
Document U.S. Pat. No. 4,486,334 (Lion) describes a process for preparing products based on a fatty acid ester, in which a fatty acid ester in the form of liquid crystals dissolved with a surfactant is cooled slowly. The cooling method is not indicated. Such a process is relatively impractical and is not modulable since it depends greatly on the capacity to form liquid crystals as a function of the surfactants.
Documents DE 4103551, WO 9213512, CA 2103578 and EP 0570398 (Henkel) describe a process for preparing products based on a fatty acid ester, in which a heated emulsion based on the fatty acid ester is cooled slowly, without flowing.
The homogeneity and kinetics of the cooling process are especially linked to the stirring conditions in the reactor. The slower the conditions of stirring of the medium, the longer and less homogeneous the cooling.
The cooling behaviour of the stirred emulsion as a whole may prove to be difficult without significant degradation of the optical properties of the concentrate. In this case, it is necessary to perform part of the cooling in the absence of any stirring to obtain concentrates of high pearlescence. This constraint induces extrapolation difficulties during industrialization of the process, and significantly impairs the production efficiency. For example, under standard cooling conditions, the industrial use of 10 to 25 m3 reactors may require from one to several days to complete this operation. Such times reveal low production efficiency. In parallel, for an equivalent formulation, the properties of the concentrates obtained industrially are generally poorer than those acquired at the laboratory scale.
There is a need for improved processes, which can satisfy at least one of the difficulties or one of the expectations stated above.